1. Field of the Invention
The present invention relates generally to vascular catheters. More particularly, the present invention relates to atherectomy catheters capable of performing abrasion atherectomy, optionally in combination with transluminal imaging.
The blood vessels of human beings commonly become constricted due to the deposition of fatty substances, e.g., lipoproteins, on the interior of the vessel walls. This condition, known as arteriosclerosis, or atherosclerosis, occurs naturally as a part of the aging process. The condition may also be promoted by such factors as heredity, diet, hypertension, and cigarette smoke. The vascular deposits result in a restriction of blood flow and in serious cases can place a person's health at risk. In acute cases the restriction can result in stroke, hemorrhage, etc. Initially, the fatty deposits are relatively soft; however, over time they become fibrotic and hardened.
Numerous approaches for reducing and removing intravascular deposits have been proposed. The deposits, called atheromas or atherosclerotic plaques, can be reshaped by dilatation of an inflatable balloon located at the distal end of an angioplasty catheter. Alternatively, atheromas can be removed from the vessel wall by cutting, grinding, or thermal ablation, e.g., via laser angioplasty. Of particular interest to the present invention are atherectomy catheters that remove atheromas from the vessel wall by cutting or grinding.
In a typical atherectomy operation, a catheter of appropriate diameter is introduced into a patient's vascular system and positioned adjacent the occluding atheroma. The distal end of the catheter is provided with a blade which is brought into contact with the atheroma. The catheter may either be a terminal (front-end) cutting type or a side-cutting type. Side-cutting atherectomy catheters frequently employ an inflatable balloon located opposite the blade to firmly engage the blade with the atheroma.
However, the above devices have certain deficiencies. In particular, the blades of the cutting element may slice into too much of the occluding material at one time, thereby causing release of large emboli and/or rupture of the vessel wall. Moreover, if the emboli are not promptly captured and removed from the patient's body, they may pass through the vascular system until they become wedged in narrow points of the vascular channels. If an embolus becomes lodged in a critical region of the vascular system, e.g., a coronary artery, the patient's health can be placed seriously at risk.
The release of large emboli into the vascular system is particularly problematic when front-end catheters are employed. Front-end devices generally employ a cutting element which extends beyond the distal end of a casing for the cutting element. See, for example, U.S. Pat. No. 4,857,046. Thus, relatively large particles can be dislodged from the atheroma. Additionally, the dislodged particles generally remain outside the casing of the cutting element, free from entrapment by the catheter. If such particles are not promptly collected they will circulate freely through the vascular system as emboli.
Side-cutting catheters generally reduce the likelihood that emboli will be released into the vascular system since the housing in which the blades are at least partially contained can passively collect dislodged particles. The collected particles can be removed from the patient's vascular system upon retraction of the catheter. See, U.S. Pat. No. 4,794,931. However, many particles can be expected to escape entrapment within the catheter in such a device.
Several methods have been proposed for remedying the shortcomings identified above. One approach is to modify the impacting head in order to channel dislodged particles into the catheter. See, for example, U.S. Pat. No. 4,857,046 which describes an auger-like mechanism for collecting particles. Another approach is to provide an aspiration means for actively removing particles from the vascular system. See, for example, U.S. Pat. No. 4,857,045. Still other approaches involve modifying the impacting head to reduce the size of the dislodged particles in an effort to minimize the risk to the patient presented by large emboli. See, for example, FIG. 4 of U.S. Pat. No. 4,857,045. None of the approaches proposed for reducing the size of particles and for capturing and withdrawing the particles provides a satisfactory solution for these problems.
For these reasons it is desirable to provide catheters that grind atheromas into very small debris particles. Also, it is desirable to remove those particles via catheters provided with flushing and aspiration means for removing the particles. Such devices are expected to significantly reduce the potential for release of large emboli. Additionally, it is desired to provide a means for transluminally imaging the site of atherectomy in order to determine the location and extent of removal of the undesired tissue.
2. Description of the Background Art
U.S. Pat. Nos. 4,857,046, 4,857,045, 4,842,578, 4,747,821, 4,631,052, and 4,795,438 all describe front-end intravascular catheter devices. None of the references describe devices that grind away atherosclerotic plaques via an impacting head that is substantially contained within a housing. Nor do the devices utilize an inflatable balloon means to aid engagement of the impacting head with the undesired tissue. U.S. Pat. No. 4,794,931 describes a catheter having a rotary impacting head which removes sclerotic material through a side window provided in a housing. An opposing balloon is provided to assist placement of the head adjacent the undesired material. U.S. Pat. Nos. 4,794,928; 4,465,072; and 3,889,657 relate to catheter designs intended to scrape blood vessels and other body lumens.
Various techniques for transluminal imaging of the diseased region of a vessel wall have been proposed, including endoscopic and ultrasonic imaging techniques. See, for example, U.S. Pat. No. 4,794,931 which describes an ultrasonic transducer attached to the hub of a rotary head. See, also, commonly-assigned copending application Ser. No. 366,906 which describes a laser catheter having transluminal imaging capability, and copending application Ser. No. 500,641 which describes a combined balloon angioplasty/imaging catheter.